This invention relates to a transfer device for use in an image forming apparatus for transferring a toner image to a copy sheet.
There have been generally known a transfer device provided with a transfer roller and another transfer device provided with a transfer belt. In the former transfer device, voltage is applied to the transfer roller upon start of an image transfer operation, and thereby a toner image formed on the surface of a photosensitive drum is transferred to a copy sheet while the copy sheet is passing through a nip between the transfer roller and drum. Further in the latter transfer device, the transfer belt is charged by a transfer charger. The charged transfer belt electrostatically attracts a copy sheet and transports the same to a photosensitive drum, and thereby a toner image formed on the photosensitive drum is transferred to the copy sheet while the copy sheet is passing through a contact portion of the transfer belt and drum.
The transfer device is provided with a brush member for removing or cleaning toner depositing on the surface of the transfer roller or belt. Upon completion of the image. transfer operation, voltage is applied to the brush member and the toner depositing on the transfer roller or belt is electrically attracted to the brush member. Thereby, the surface of the transfer roller or belt is cleaned.
However, the transfer device is provided with a power supply unit for applying power to the transfer roller or belt and another power supply unit for applying power to the brush member. Provision of two power supplies has been an obstacle to higher cost effectiveness and has required larger space.